City of Punta Gorda Adaptation Plan Southwest Florida Regional ...

Thunderstorms and High

Thunderstorms and High Winds A thunderstorm is formed from a combination of moisture, rapidly rising warm air, and a force capable of lifting air such as a warm or cold front, a sea breeze, or a mountain. All thunderstorms contain lightning. Thunderstorms may occur singly, in clusters, or in lines, thus, it is possible for several thunderstorms to affect one location in the course of a few hours. Some of the most severe weather occurs when a single thunderstorm affects one location for an extended time. Although the average Florida thunderstorm is less than 15 miles in diameter, they can grow vertically to great heights in excess of 10 miles into the upper atmosphere. This stacking effect of concentrated moisture can explain why a Florida thunderstorm directly overhead could produce four or more in less than one hour while a location only a few miles away may receive just a trace (NWS). Thunderstorms are capable of producing two kinds of damaging winds. The first is tornado winds, which are rotational in character. The second is downburst/gust front winds, which are straight-line in character. In Florida, occurrences of damaging downburst winds outnumber tornado winds by nearly 10 to 1. A typical gusty breeze around 25 mph accompanied by a temperature drop of 10 to 20 degrees in a few minutes of time is the result of the downdraft of a nearby thunderstorm. However, at times, this downdraft becomes more vigorous and can become a downburst. Downburst winds can become severe, reaching speeds in excess of 58 mph and causing considerable damage. In extreme cases, some downburst winds can be as strong as an F2 tornado (NWS). While thunderstorms and lightning can be found throughout the United States, they are most likely to occur in the central and southern states. Map 3 in Appendix D shows the average number of thunderstorm days each year throughout the U.S., with Florida having the highest incidence (80 to 100+ thunderstorm days per year). It is in this part of the country that warm, moist air from the Gulf of Mexico and Atlantic Ocean is most readily available to fuel thunderstorm development (National Weather Service). Heavy rains (which can cause flash flooding), strong winds, hail, lightning and tornadoes are all products of thunderstorms. Lightning is a major threat. Each year 75 to 100 Americans are hit and killed by lightning, According to the National Weather Service, damaging wind from thunderstorms is much more common than damage from tornadoes. In fact, many people confuse damage produced by ―straight-line‖ winds attributing it to tornadoes. Wind speeds can reach up to 100 mph (161 km/h) with a damage path extending hundreds of miles. Damaging winds are classified as those winds exceeding 50-60 mph (80-100 km/h) (NWS). Increased air and water temperatures related to climate change may result in stronger, more frequent thunderstorms. It is one of the paradoxes of climate change that ―rains will be rainier and droughts will be droughtier‖, but the increased intensity of storms will have many consequences. These stronger storms will contribute to more coastal as well as inland erosion along rivers and creeks, urban and suburban erosion from stormwater runoff, and urban and suburban flooding. AdaptationPlan Page 300

According to NOAA (2007), 60 significant thunderstorm/high wind events were recorded in Charlotte County between January 1, 1950 and September 30, 2004. These events resulted in 0 deaths and 8 injuries. An estimated $1.0 million in property damage is attributed to these events. Following is a brief description of the 8 thunderstorm/high wind events that have recorded by NOAA (2207) in Charlotte County since January 1, 2000. August 1, 2000, PuntaGorda: The Charlotte County Sheriff‘s Department reported that thunderstorm winds downed several large trees, branches, and power lines near the intersection of U.S. Highway 17 and Cleveland Drive in PuntaGorda. Approximately $10,000 in property damage was associated with this event. August 6, 2000, Countywide: The Charlotte County Emergency Management reported that thunderstorm winds downed several large trees, downed numerous large branches, and power lines across the county. Damage estimates associated with this storm reached $100,000. June 5, 2001, Englewood to PuntaGorda: Florida Power & Light utility and the public reported that a few large trees, branches and powers lines were downed by thunderstorm winds from Englewood to PuntaGorda. Damage estimates associated with this storm reached $20,000. June 16, 2001, Port Charlotte: Charlotte County Emergency Management reported that thunderstorm winds downed a few large trees, large branches and power lines in Port Charlotte. Damage estimates associated with this storm reached $5,000. July 10, 2001, PuntaGorda: Thunderstorm winds caused minor damage to a few homes and downed several large branches on Riverside Drive in the River Forrest mobile home park in PuntaGorda. Damage estimates associated with this storm reached $10,000. March 2, 2002, Countywide: A departing high pressure system combined with an approaching cold front to produce strong and gusty south winds across the central coastal counties from late morning through the afternoon. Sustained winds ranged from 25 to 30 mph, with a period of gusts in excess of 40mph between noon and 2 pm. The winds enhanced a small brush fire along highway 41 in Charlotte County. Property damage was reported at $7,000 for this event. June 28, 2003, PuntaGorda: Thunderstorm winds damaged a pool cage and part of a roof. This damage was estimated at$3,000. April 12, 2004, Regional: AdaptationPlan Page 301